Water-cooled nuclear reactors, especially pressurized-water nuclear reactors, comprise a vessel which is intended for containing the core of the nuclear reactor and which is connected to the cooling circuit of the reactor in which the cooling water circulates.
The wall of the reactor vessel, which is in contact with the cooling fluid and which is exposed to the radiation emitted by the reactor core, can become highly contaminated after the reactor has been operating for some time.
As regards nuclear power stations which have reached the end of their useful life and which need to be shut down completely, the solution adopted in the past has been to leave these power stations in their existing state and to allow the activity of the constituent materials of their components to decrease, in order to dismount them at a later data under more satisfactory conditions than at the time of the shutdown, without the need to use complex remotely controlled tools.
A substantial increase in the number of power stations put out of industrial operation is to be expected in the future, and therefore it is necessary to consider dismantling these power stations so as to restore the site where they are built to its original state.
The dismantling of the conventional part of the power station presents no particular problem, but in contrast the dismantling of the part of the power station forming the actual nuclear reactor raises problems which are difficult to solve because of the radioactive emissions of the constituent materials of the reactor components.
In particular, the vessel of water-cooled nuclear reactors, which contains the fuel assemblies and which is in contact with the cooling water of the reactor during its operation, is very highly contaminated in the case of reactors which have reached the end of their useful life.
As regards to pressurized-water nuclear reactors currently in operation, the reactor vessel takes the form of a body of generally cylindrical shape closed by domed bottoms, of large size and having a large wall thickness.
The vessel, which has a very high mass, is arranged inside a vessel well formed in a concrete structure which also delimits one or more pools located above the upper level of the vessel.
The vessel, which contains various internal structures in addition to the fuel assemblies, is connected by means of connection pieces to pipelines of the primary circuit of the reactor.
The core assemblies and some components of the internal structures can be dismounted and taken out of the vessel, in order to obtain their removal and, where appropriate, their elimination, at the time when the reactor is put out of operation.
To date, there have been no known processes and devices for safely dismantling the vessel of a pressurized-water nuclear reactor and in particular makes it possible to avoid risks of radioactive contamination in the work zone, while at the same time using machining and handling means of relatively simple structure to effect the removal and elimination of the material of the vessel.